Gymnocladus dioica

Gymnocladus dioica is a tree native to North America, particularly Canada where it is commonly called Chicot or Bonduc. Still little known and planted in our gardens, it is nevertheless very interesting for its foliage with changing colours which gives it a beautiful exotic appearance. Its young leaves, which emerge late in spring, are pink and turn green in summer, at the same time as fragrant clusters of flowers appear. They turn golden yellow before falling very early in autumn, so it has a singular silhouette of a dead tree for much of the year. Extremely hardy, it is an excellent light shade tree for a large garden. It can be grown in a small garden with regular pruning.

Gymnocladus dioica (syn. Guilandina dioicus or Gymnocladus canadensis) belongs to the Fabaceae family and the subfamily Caesalpinioideae. It is sometimes called the boneset tree, and in English it is called the Kentucky coffee tree, because its seeds were once roasted and used as a coffee substitute. It is found in southern Ontario, Canada, and in Kentucky where it was discovered by Europeans, as well as in a large part of the eastern United States. It is highly appreciated and often planted as a shade tree in North America. The Kentucky coffee tree grows in floodplains and near watercourses, but it can also be found on rocky slopes and in forests on limestone soil. In fact, this tree could be an indicator of limestone soils.

It is a tree of medium to large size, with slow growth in its early years. Its habit is rather spreading, forming an oval to rounded, irregular, semi-open crown. At maturity, it will reach about 18 metres (59ft) in height and 15 metres (49ft) in width if not regularly pruned. Its trunk, which can be multiple or single, is covered with a dark grey, rough, channelled and scaly bark, which is quite decorative, and its young branches are grey. The deciduous foliage is composed of doubly pinnate leaves, with 3 to 8 pairs of pinnae, each composed of 6 to 14 ovate leaflets. These immense leaves reach 80cm (31.5in) to 1m (3 in 4ft) in length and 50 to 60cm (19.7 - 23.6in) in width. Bud-break is late, with the young leaves not emerging until May-June, tinted with reddish-copper. They generally fall off at the beginning of October. Gymnocladus dioica has both male and female individuals. The flowering occurs in June, in the form of clusters of honey-scented and fragrant papilionaceous flowers. The female flowers are grouped in clusters 20 to 30cm (7.9 - 11.8in) long, with 5 reddish sepals and 4 to 5 cream-coloured petals. The male flowers, on the other hand, are gathered in clusters 8 to 12cm (3.1 - 4.7in) long. The fruit is a large, hard, oblong pod that turns dark brown when ripe and opens into two valves. Each pod, which can reach 20 to 25cm (7.9 - 9.8in) in length, contains several seeds surrounded by sweet pulp. To be consumed, these seeds must be roasted beforehand. Its roots are both deep, in the form of taproots, and spreading: this Gymnocladus should be kept away from buildings and ducts.

This Kentucky coffee tree is naturally well adapted to large gardens, where it will provide very pleasant shade. It tolerates urban pollution and is particularly suitable for limestone and fresh soils, as well as loamy or sandy soils. It is found as an ornamental tree in parks and along certain avenues. You can place it against a backdrop of evergreen shrubs or conifers (cypresses, thuja, yew, junipers). It can also be associated, in a flowered grove and in very fresh soil, with the Toona sinensis 'Flamingo' or the Robinia pseudoacacia 'Frisia' or Gleditsia triacanthos 'Rubylace'.